The present invention relates to positive displacement hydraulic pumps of the vane type, and more particularly, to an improved discharge port arrangement for such pumps.
It will become apparent to those skilled in the art from a reading of the present specification that the invention may be used with any type of vane pump, but it is especially advantageous when used in a pump in which the vanes are configured such that radial movement of one of the vanes changes the volume of the adjacent fluid chamber. Therefore, although the invention could be utilized with certain types of slipper vane pumps, the invention appears to have its greatest advantage when used with roller vane pumps, and it will be described in connection therewith.
Pumps of the type to which the present invention relates are shown and described in detail in U.S. Pat. No. 3,025,802, assigned to the assignee of the present invention. Typically, such pumps include a housing defining a pumping chamber, and a pumping element rotatably disposed in the pumping chamber and defining expanding and contracting fluid chambers. The housing means defines a fluid inlet port in communication with the expanding fluid chambers, and a fluid outlet port in communication with the contracting fluid chambers. The pumping element includes a rotor member mounted for rotation with an input shaft, the rotor member having a plurality of slots. Each of the slots receives a radially displaceable vane member which is configured such that radial movement of the vane member changes the volume of the adjacent fluid chamber. The pumping chamber is defined by a continuous arcuate wall surface including an inlet arc surface of progressively increasing radius in the direction of rotation of the rotor member, and a discharge arc surface of progressively decreasing radius.
In pumps of the type described, the housing defines an intake port which permits fluid communication between the fluid inlet port and the expanding fluid chamber, and a discharge port which permits fluid communication between the contracting fluid chamber and the fluid outlet port.
One of the primary problems associated with pumps of the type described is the generation of undesirable pressure pulses during the pumping cycle. Such pulses may be transmitted through the hydraulic lines to the vehicle steering gear which can then translate the pressure pulses into noise, audible to the driver. Pressure pulses and noise emanating from the pump can be generated in several ways, and it has long been an object of those skilled in the art to identify and eliminate such sources of noise and pressure pulses.
Those skilled in the art have for a long time recognized that one of the primary causes of pressure pulses is incorrect timing of the fluid communication between the fluid chambers of the pumping element and the intake and discharge ports. For example, if a trapped volume of pressurized fluid remains in a fluid chamber, just as that chamber begins to communicate with the intake port, the result will be a flow from the fluid chamber into the intake port, in opposition to the normal flow path from the intake port into the expanding fluid chambers. Such a condition will result in flow turbulence and pressure pulses.
Those working in the art have proposed solutions to the readily identifiable errors in the timing of the fluid communication. See for example U.S. Pat. Nos. 3,025,802 (assigned to the assignee of the present invention), and 4,080,124. Many such solutions have proven helpful, and are now being recognized and accepted as good state of the art pump design.
However, pressure pulses and pump noise remain a persistent problem despite such attempts to eliminate all of the readily identifiable timing errors and sources of noise.
Accordingly, it is a primary object of the present invention to identify and eliminate additional sources of pressure pulses and noise which have been previously unrecognized.
During the development of the subject embodiment of the invention, it was observed that there is a slight increase in the volume of the contracting volume chamber, and a small amount of flow into the contracting volume chamber, during the initial portion of the cam "fall", i.e., the period during which the contracting fluid chamber moves along the discharge arc surface.
Accordingly, it is another object of the present invention to identify the cause of this increase in volume of the contracting fluid chamber, and determine its effect upon proper timing of fluid communication between the contracting fluid chamber and the discharge port.
It is a more specific object of the present invention to provide a rotary fluid pump of the type described above in which the discharge port design and location take into account the above-noted increase in the volume of the contracting fluid chamber.
The above and other objects of the present invention are accomplished by the provision of an improved rotary pump of the type described above. Each vane member, being referred to as a leading vane member as it progresses across the discharge arc surface, cooperates with a trailing vane member and the discharge arc surface to define the contracting fluid chamber. The volume of the contracting fluid chamber is simultaneously increased by the radially inward displacement of the leading vane member, and decreased by the progressively decreasing radius of the discharge arc surface.
The improvement of the present invention comprises the discharge port being located, relative to the discharge arc surface, such that communication between the discharge port and the contracting fluid chamber begins at the point at which the decrease in the volume of the contracting fluid chamber, caused by the decreasing radius of the discharge arc surface, approximately equals the increase in the volume of the contracting fluid chamber caused by the radially inward movement of the leading vane member. This particular design and location of the discharge port substantially prevents communication between the contracting fluid chamber and the discharge port until the contracting fluid chamber has undergone a net decrease in volume, with continued rotation of the pumping element, thus substantially reducing fluid turbulence and pressure pulses.